Once overlooked by many fly fishers, Caddis Flies are now known to be an extremely important food source for trout. This is due to their condensed annual hatches and survival by numbers approach to life. The most prominent Caddis hatches can be seen moving up river in a swarm. There are three basic forms of Caddis flies: Adult Caddis Flies, Emergers and Nymphs or Larva. The Caddis fly is present in the trout stream in one of these forms most of the year.